1. Field of the Invention
The present invention relates to new catalysts for the oxidation of unsaturated aldehydes to produce carboxylic acids and to methods of making and using such catalysts. More particularly, this invention relates to mixed metal oxide catalysts for the oxidation of unsaturated aldehydes, such as acrolein, to produce the corresponding alpha-beta unsaturated carboxylic acids, i.e., acrylic acid.
2. Description of the Prior Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
The vapor phase oxidation of acrolein for the production of acrylic acid is known in the art. Various references disclose the use of mixed metal oxide catalysts containing molybdenum and vanadium, alone or in combination with other metals, for use in the catalytic oxidation of acrolein. The following is a brief summary of the disclosures of several of these references.
Japanese Patent Publication No. 11343261 discloses the preparation of acrylic acid by catalytic oxidation of acrolein in the presence of a metal oxide catalyst. The catalyst has the formula MoViSbjAk, wherein A is Nb or Ta, i and j are 0.01–1.5, the ratio of j to i is 0.3–1.0, and k is 0.001–3.0. Acrolein is oxidized in the presence of oxygen and the metal catalyst at 260° C. and a contact time of 0.95 seconds, wherein the ratio of Mo:V:Sb:Nb is 1:0.3:0.23:0.08. A 97.2% yield of acrylic acid is achieved.
German Patent Publication No. 19815281 describes the preparation of molybdenum and/or vanadium containing mixed metal oxide catalysts for the partial oxidation of acrolein to acrylic acid. The mixed metal oxide catalysts have the formula ApBqCr, wherein A is Mo12VaX1bX2cX3dX4eX5fX6gOx, B is X7CuhHiOy, C is X8SbjHkOz, X1 is W, Nb, Ta, Cr, and/or Ce, X2 is Cu, Ni, Co, Fe, Mn, and/or Zn, X3 is Sb and/or Bi, X4 is Li, Na, K, Rb, Cs and/or H, X5 is Mg, Ca, Sr, and/or Ba, X6 is Si, Al, Ti, and/or Zr, X7 is Mo, W, V, Nb, and/or Ta, X8 is Cu, Ni, Zn, Co, Fe, Cd, Mn, Mg, Ca, Sr, and/or Ba, a is 1–8, b is 0.2–5, c is 0–23, d is 0–50, e is 0–2, f is 0–5, g is 0–50, h is 0.3–2.5, i is 0–2, j is 0.05–50, k is 0–50, the values of x, y, and z depend on the valence and relative abundance of the remaining elements in the composition, and p, q, and r are greater than or equal to zero, with the proviso that p/(q+r) is 1–20. The mixed oxide catalysts are prepared from finely ground precursor components which are mixed, dried, and calcined at 250–500° C.
European Patent Publication Nos. 774297, 711745, 0685259, 427508, and 293859 relate to the use of mixed metal oxide catalysts containing molybdenum and vanadium in the gas phase oxidation of acrolein. WO 9627437 discloses the manufacture of a highly active catalyst having high mechanical strength suitable for the gas phase oxidation of acrolein. The catalyst contains molybdenum, vanadium, copper, and antimony as essential components. Similarly, U.S. Pat. No. 4,289,654 describes the use of a mixed metal oxide catalyst containing molybdenum, vanadium, tungsten, copper, and chromium on an alpha alumina support to oxidize acrolein to acrylic acid at 97% selectivity.
Japanese Patent Publication Nos. 05329371 and 05317713 relate to the production of a highly selective catalyst for acrolein oxidation. The catalyst is produced from a catalyst precursor containing molybdenum and vanadium, among other components. Japanese Patent Publication No. 04321642 describes the use of a molybdenum and vanadium based metal oxide catalyst to oxidize acrolein in the gas phase. The catalyst has the formula MoaVbSicNadAeXfYgOh, wherein A is Fe, Cr, Co, and/or Sr, X is Ge, Se, Sn, Te, and/or Sm, Y is Mg, Ti, Cu, Zn, Nb, Mn, Ni, Ag, Ta, Bi, Ce, and/or W, and a, b, c, d, e, f, and g are integers, such that the ratio of one to the other is a:b:c:d:e:f:g or 12:(1–6):(0.1–15):(0–2):(0.1–3):(0.1–3):(0–3),and h is an integer which satisfies the valance of the remaining elements of the composition. The patent describes the use of such a catalyst (having a formula Mo12V3Si4FeGe0.2Oh) with a gas mixture of 5% acrolein, 10% oxygen, 30% steam, and 55% nitrogen at 270° C. to yield acrylic acid with 95% selectivity and at 99% conversion of acrolein.
Soviet Union Patent Publication Nos. 858916 and 899112 describe a catalyst containing vanadium oxide and molybdenum oxide, and copper oxide as a promoter on a silica support suitable for acrolein oxidation to acrylic acid. The catalyst exhibits increased activity and mechanical strength due, at least in part, to its method of manufacture. The catalyst is prepared by granulating the catalyst material after drying and adding promoter and a binder compound during granulation. Great Britain Patent Publication No. 1586173 discloses the use of metal oxide catalysts containing molybdenum, vanadium, chromium, copper, and a metal selected from Mb, Ta, and/or Ti, for the oxidation of acrolein to acrylic acid with improved conversion and selectivity. The ratio of molybdenum, vanadium, chromium, copper, and the metal is Mo:V:Cr:Cu:M or 15:(5–7):(0.7–0.8):(2.4–2.8):(1.5–2). A feedstock containing 5.6 mol % acrolein, 30 mol % nitrogen, and oxygen was passed through the catalyst and heated to 300° C. in a 3.05 m×2.54 cm stainless steel pipe reactor. At a contact time of 2.9 seconds, 99% of the acrolein was converted to acrylic acid at a selectivity for acrylic acid and carbon oxides of 93.4% and 4.4%, respectively.
The catalysts described above exhibit decreased stability over time (see European Patent Publication No. 0711745, Japanese Patent Publication No. 25914, and Cat. Rev. Sci. Eng., vol. 35, p. 213 (1993)). This is due to the generation of V2O5, which is responsible for the slow decay of the catalyst performance. Therefore, it would be desirable to develop a molybdenum and vanadium based catalyst for the production of carboxylic acids from aldehydes which would exhibit enhanced performance and stability.